Referring now to U.S. Pat. No. 4,066,243 (Johnson), a jack for the use with automobile bumpers is shown, in which a frame is provided as a support means for a vertical pipe, which has a sleeve, which moves upward and downward around said pipe. A typical floor jack provided the upward lifting force against the sleeve, where the floor jack was attached to the sleeve portion through a ring. This device required a secondary jack, and was limited to the lifting of a vehicle body parts which would comprise a bumper.
Referring now to U.S. Pat. No. 4,123,038 (Meyers), an apparatus is disclosed in which an elaborate load bearing frame is provided, where the apparatus operates using two separate hydraulic jacks. There is no realistic application of this type of device with a small tractor or riding lawn mower.
Portable jacks for small tractors are specifically exampled in U.S. Pat. No. 4,549,721 (Stone), in which a screw-scissors jack was operated to provide lifting force against a framework so as to push the framework upward. It would appear that one of the drawbacks of this invention was that the framework had a rectangular configuration, which would create a problem where a portion of the framework had to be moved under the tractor front wheels. This requirement would present a problem in a situation where the tractor was unable to move under its own power, requiring physical work to move the tractor over the framework assembly. Further, this device would not work properly at a location where the ground on which the tractor was situated was not properly leveled.
Referring now to U.S. Pat. No. 5,358,217 (Dach), the lifting apparatus is disclosed, in which a framework had a narrow front end, and avoided some of the problems inherent in the Stone patent referenced above. This system required a hydraulic cylinder to provide an upward pushing force to lift the item or vehicle. Extended arms had curved metal prongs that were referenced as lifting points. This jack was not intended for use with small tractor wheels, but rather were intended for axle assemblies.
Referring now to U.S. Pat. No. 6,474,626 (Box), a rack for securing a lawn mower to an elevated position is shown, in which a cage-like framework assembly is provided, and where a flexible webbing is used with a wheel crank to pull the entire lawn mower into an elevated position. This assembly is similar to an automobile rack, with the exception that the lifting framework is rectangular in nature, and supports all four wheels of a push mower on rack.
Further patents have disclosed jacking mechanisms with riding lawn mowers. U.S. Pat. No. 6,516,597 (Samejima et al.) discloses a lawn tractor which allows manipulation of its wheel supports into position so that they can be used to assist in raising up the front end of the lawn tractor.
Referring now to U.S. Pat. No. D 468,512 S (Hernandez), an all-terrain vehicle lift is disclosed, in which a hydraulic cylinder is used, to lift a metal framework that is disposed at the front end of the apparatus. The invention uses a rectangular frame, and a support means for the wheel is limited to a single tire, and not to two wheels, unless they are fairly close together.